Hurricane Idalia, which has triggered evacuations as it threatens to pummel the northern reaches of Florida, is being fueled by unusually high temperatures in the Gulf of Mexico, part of a trend of extreme marine heat that has dominated the summer.
Idalia has churned across the Gulf of Mexico as a category 1 storm but is expected to strengthen to a category 3 event by the time it crunches into Florida’s western coast on Wednesday, making it the first hurricane to hit the US this year.
The rapid intensification of the hurricane, which is expected to bring strong winds, rain and a storm surge of up to 12ft as it travels across northern Florida, has been spurred by ocean temperatures that have remained persistently elevated throughout the summer.
The eastern parts of the Gulf of Mexico have been around 87F (30.5C) to 89F (31C) in recent days, several degrees above the long-term average and part of a vast network of marine heatwaves that have covered nearly half of the world’s oceans this summer. Scientists have said the extreme oceanic heat is consistent with the expected impacts of the climate crisis.
The exceptional warmth of the Gulf extends down to about 165ft below the surface of the area where Idalia is traveling through, a rare occurrence described as “other-worldly” by Andy Hazelton, a scientist at the National Oceanic and Atmospheric Administration (Noaa).
This level of ocean heat alone would be enough to make Idalia a devastating category 5 storm, scientists have said, although other factors such as wind shear will influence the ultimate outcome of the tempest. Hurricanes gather strength from warm oceans and moisture in the atmosphere, which are both facets of global heating.
Studies have shown there is evidence that Atlantic hurricanes are becoming stronger and intensifying more rapidly due to these accelerants provided by the climate crisis. The current naturally occurring El Niño climate phenomenon, which has heated up the equatorial Pacific Ocean, is normally associated with a weaker hurricane season in the Atlantic, but Noaa recently warned of an above-average period of storms due, in part, to the extreme heat that has accumulated in the oceans.
The oceans have absorbed about 90% of the extra heat due to the release of greenhouse gases from burning fossil fuels, with the heightened temperatures causing stress to fish and bleaching and even death to coral reefs.
Prof Michael Mann of the University of Pennsylvania told CNN: “We have bathtub-level warmth with these waters in the Caribbean and the tropical Atlantic … It’s been the warmest year we have ever seen when it comes to Atlantic Ocean temperatures and global temperatures as well.”
In July, the waters off southern Florida were measured to be at 101F (38F), a record temperature more often found in Jacuzzis than the ocean that raised fears for the state’s ailing coral reef.
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A “heat dome” – an area of rigid high pressure that locks in repeatedly high temperatures – has squatted over parts of the US south this summer and brought extreme heat to coastal areas as well as the oceans. Over the weekend, both Houston and New Orleans recorded their hottest temperatures ever measured, reaching 109F (42C) and 105F (40.5C), respectively.
Mann said the ocean temperatures were partly the natural transition to El Niño but added: “[It] is riding on the top of this tide of an ever-warming planet from carbon pollution, from the burning of fossil fuels, and that heat is not just at the surface, it’s penetrating deeper into those ocean layers and that’s when you see … these rapid intensification events.”
Mann said El Niño weather systems lead to more wind shear, which “tends to interfere with hurricanes”, so experts had thought this would be an average or just above average year for storms, but the record ocean temperatures were changing that picture.
“Excessive warmth is overcoming the typical dampening effect of the El Niño event … Conditions right now are going to support those major, monster cat[egory] 4 and cat[egory] 5 hurricanes if they have a chance to form.”
